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    <title>Document</title>
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    <script>
        var arr = [1,2,3,4];
        console.log(arr.join(''));//1,2,3,4
        console.log(arr.join());//括号里不填是逗号分隔 '1,2,3,4'
        console.log(arr.join('-'));//括号里不填是逗号分隔   '1-2-3-4'
    </script>
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